Flexible backed abrasive and method of making the same



Jan. 18, 1944. Q MARTlN 2,339,500

' FLEXIBLE BAGKED ABRASIVE AND METHOD OF MAKING THE SAME Filed Feb. 13, 1942 5 Sheets-Sheet 1 Elven-Ear,

-- HAEBY C M48770 Jan. 18, 1944. R-rm 2,339,500

.FLEXIBLE BACKED ABRASIVE AND METHOD OE MAKING THE SAME Filed Feb. 13, 1942 5 Sheets-Sheet 2 TO 0315 g WWW Jan. 18,1944. M T N 2,339,500

FLEXIBLE BACKED ABRASIVE AND METHOD OF MAKING THE SAME Filed Feb. 13, 1942 v 3 Sheets-Sheei 3 Elven-79077 35 {'1 1, Hneev c. finer/H Patented Jan. 18, 1944 FLEXIBLE BACKED ABRASIVE AND METHOD OF MAKING THE SAME Harry C. Martin, Niagara Falls, N. Y., assignor to The Carborundum Company, Niagara Falls, N. Y., a corporation 01' Delaware Application February 13, 1942, Serial No. 430,800 3 11 Claims. ('01. 51-195) This invention relates to the manufacture of backed abrasives, and in particular to the manuiacture of backings for abrasive disks and belts in which the backings are composed of a tough and flexible but comparatively cheap material.-

Backings for abrasive disks and belts have been made in many cases from a comparatively expensive main constituent known as vulcanized fibre. This material can be manufactured, for example, by pulping and sheeting pure cotton which is then subjected to the action of a solution of zinc chloride. This solution dissolves part of the fibre and leaves a gelatinous, sticky coating on the outside of the fibres. The sheets of this fibrous material are compressed between'rolls and subsequently washed to remove as far as possible the last traces of zinc chloride and then dried. The drying is accompanied by considerable shrinkage. In view of the cost of theoriginal pure cellulosic material and in view of the large number of successive treatments to which the cellulose fibres have to be subjected the cost of the vulcanized fibre is high. Many substitutes for vulcanized fibre" have beentrled in order to avoidthe cost of this expensive material. Difiiculties have arisen in the course of such attempts because abrasive disks and belts are subjected to severe mechanical stresses in operation. The disks are mounted, for example, on flexible pads driven by motors of several: horse-power capacity. The mounted'abrasive disks are used in such applications as the grinding down of sharp tough weld seams. Abrasive diskbackings formed of many of the cheaper substitutes for vulcanized fibre split both radially and concentrically and thus constitute a hazard to the safety ing abrasive disks and belts by adding to at least one of the faces of each successive layer of paper a glue or adhesive, while the layers are still moist, and then combining the layers to form a laminated paperboard stock.

A secondmethod of strengthening paperboard made from highly hydrated krait pulp is, to ap-. ply a layer of adhesive to one side or both sides of the partly dried laminated sheet as it is being processed through the drying rolls of the paper machine. When a suitable amount of the proper adhesive is so applied the resulting'sheet is found I .lustrate the accompanying specification.

Figure 1 is a schematic view of the wet end of a five vat cylinder .paper making machine proof workmen. The belts receive severe flexing in bed plate and does not cut the pulp. The fibre length is thus'retained and the resultant sheet is flexible. Pulp of the kind just described can be formed into thin webs on .a paiefmachine of the cylinder type and a laminated paperboard stock made with a total thickness 'of a hundredth of an inch or a little more (0-.010-0.018 inch).

It has further been found that the strength of the paperboard is much improved for use in makvided with means for-applying adhesive between laminations of the paper;

Figure 2 is a side elevation showing part of of one modification of the disk of the present invention;

Figure 8 is an enlarged view in cross-section of another modification of the disk of the present invention and Figure 9 is an enlargedview in cross-section of one modification of an abrasive belt made according to the present invention.

The principal backing constituent for the abrasive disks and belts of the present invention is obtained fromkraft pulp. Kraft pulp is a wood pulp made by a chemical'caustic cooking process. This process differs from the soda proces in the addition of sodium sulphide. In carry- Figure 7 is an enlarged view in cross-section ing out the mechanical hydration, kraft pulp is beaten for 30-40 hours in a conventional paper mill beater with the beater rolls adjusted to exert extremely light pressure and not to cut the fibres appreciably. This type of beater treatment serves to hydrate and gelatinize the cellulose fibres. The

to a paper machine such as that shown in Figure 1.

Referring to the drawings, and first to Figure 1,

there is shown diagrammatically the wet end of a five vat cylinder paper making machine, having means for applying an adhesive to the interfaces between laminations of the paper produced thereby, to carry out the first and third modifications of the method set out above. The vats are shown as V1 to V5, each vat having a cylinder mold therein and a couch roll above the cylinder mold. Each vat is filled to a suitable level with stock consisting of highly overbeaten kraft pulp and water. In vat V1 the cylinder mold is designated M1 and the couch roll C1. The conventional felt F travels between the cylinder mold M1 and its couch roll C1, picking up a thin layer of pulp or paper on the bottom of the felt as it passes over mold Mi. As the felt and the one adhering layer of pulp or paper passes mold M2, the layer ventional mechanism, not shown, which applies a second travelling felt to the bottom surface of the paper, and the paper is squeezed and dried between the felts until it becomes self-sustaining, at which time it leaves thefelts and travels to the drier rolls shownin Fig. 2.

When the strengthening of the paper is accomplished only by an outer layer or layers of adheshown near the end of its course through a drying arrangement comprising heated rolls 8. Two

adhesive applicator means are shown one for applying adhesive to each side of the partly dried sheet. One of these means may be omitted if the sheet is to be coated on one side only. The upper coating means comprises a trough 9 containing adhesiv solution In. Roll H dips into the solution, transfers adhesive to roll I2,- which in turn transfers it to applicator roll l3.1 The lower coating means is similar to the upper one except that the intermediate roll is omitted. The

- adhesive can be a warm glue solution at a temof wet paperon the felt picks of! another layer of paper. The process continues as the felt and paper pass molds M3, M4, and M5, the resulting paper consisting of 5 layers, one produced by each mold. It is obvious that a paper of any desired number of layers may be made by employing that number of cylinder molds. The number of molds shown in the drawings is chosen for convenience only, and is not to be construed as a limitation.

Between each pair of adjacent vats there is located a means of applying a suitabieglue or adhesive to the exposed face of the lowermost layer of paper on the felt, for the purpose of securing improved adherence between layers and improving the strength and endurance to repeated flexure of the resulting paper. The adhesive applying means consists of a trough I containing a suitable adhesive solution which may be a warm glue solution at a temperature of about 120 F. and containing 10-15% by weight of dry, high grade hide glue. Roll 2, which dips into the adhesive solution, and roll 3, which transfers the adhesive from roll 2 to the paper layer, are power driven so that roll 3 has the same peripheral speed as the paper layer it contacts, to avoid any detrimental strain-on the weak paper layer. The felt F is backed up, at a point opposite roll 3, by idler roll 4. The rolls 2 and 3 and the container I can be adjusted vertically relatively to each other and as an assembly to regulate the amount of adhesive applied to each layer and also the amount of pressure which roll 3 exerts on the I paper layer. When the felt passes mold M5, the paper adhering to its underside consists of 5 layers with a layer of adhesive between each two adjacent paper layers. The, felt and the adhering wet laminated paper then passes through an extractor press consisting of rolls 5 and 6, top roll 6 being a rubber covered roll and roll 5 being a wire faced hollowroll to receive water from the paper. -The paper, still on felt F, passes to conperature of about 120 F. and containing 10-15 percent by weight of dry high grade hide glue. The rolls of the adhesive applicator means can be'adjusted to apply sufiicient adhesive so that when the coating is dried the glue/left on each side of the sheet is about 1.5 percent of the weight of the final sheet when there is a ten percent glue solution in the containers 9. If a more concentrated glue solution, for example 15 per cent, is

- in the containers 9, the percentage of dry glue in the coated sheet may be as much as 2.3 percent by weight of the final sheet. Various other adhesives may be substituted for the hide glue above or less, subsequent heated drier rolls 8. is sufficient to dry the hide and casein glues and to partially harden the urea resin and the phenolic resin. Hardening of these two resins is completed duringthe curing of the abrasive bond of the product. After passing the five drier rolls, the sheet] goes to the calender rolls for finishing.

The highly hydrated pulp stock produces a paper in which the individual fibers are strongly interlocked. Hydrated cellulose is a gelatinous fluid and the prolonged beating of the pulp stock results in the formation of a coating of hydrated cellulose on the outer surfaces 01' e ch fiber byreason of the hydration of those parts of the fibers. When a sheet is formed from such fibers,

the gelantinous hydrates flow together with the result that the cellulose fibers which go to make up the paper sheet and which are reformed when the material is dehydrated, are so interwoven and interlocked that the resulting paper is un-' usually tough and strong.

Since the adhesive employed between laminations and on one or both outer surfaces of the slieet is applied while they are quite'moist, it' I penetrates the sheet to a considerable extent, strengthening it to a marked degree by bonding the fibres of the paper laminations together and the lamination's to each other. When it is desired to obtain even better penetration of the adhesive, however, a wetting agent may be mixed with it. Such wetting agent may be, for example, a sodium salt of sulfonated succinlc acid, suchas diamyl ester of sodium sulfosuccinic acid, dibutyl ester of sodium sulfosuccinic acid, dihexyl ester of sodium sulfosuccinic acid; or dioctyl ester of sodium sulfosuccinic acid, or it may be alkyl aryl sulfonate. I

It is sometimes desired to tan the hide glue or the casein glue after its application to the -sheet, to improve its resistance to moisture. In such case, the'sheet is passed, about four drier rolls further on from the second outer adhesive layer applicator, through a tanning solution I such as a potassium bichromate solution or a formaldehyde solution, held in container 3' into which roll 8' dips. The outer layers of glue are thus wet by the tanning solution, and some of said solution penetrates to the inner layers of glue between paper laminations. The sheet then passes around further heated drier rolls, and when dry is forwarded to the calender rolls.

As an alternative to tanning the glue, as above, the glue between paper laminations may be waterproofed by adding methyl abietate thereto. In one example of this method, methyl abietate in the amount of 1025% by weight based ,on the weight of-the dry glue is added to a water solution of animal glue. The resulting mixture is employed as the adhesive between laminations' of the paper, and may be contained in troughs I and applied by rolls 2 in the apparatus shown in Fig. 1.

In Fig. 3 the roll I! contains a supply of paperboard which has passed through the apparatus shown in Fig. 2. The container liholds a glue solution from which a'layer of glue is applied to one side of the paperboard; this sidemay or may not have been previously coated with adhesive while still moist by the apparatus shown in Fig. 2. The roll l6 contains a supply of cloth, such as light print cloth. The travelling cloth meets the travelling paperboard under the roll I! and the two travelling sheets become united by means of the fresh layer of adhesive on the paperboard. The combined sheet then passes on to a drier.

In Figure 4 there is shown diagrammatically apparatus for coating the combination backing sheet .with abrasive particles. Thelroll fl8 contains a combination backing sheet formed by the union of'paperboard'adhesively attached to cloth.

The travelling combination sheet receives a layer of liquid adhesive from the container IS on the cloth side of the combination sheet. Shortly thereafter abrasive particles are dropped on the adhesive layer by means and the abrasivecoated sheet passes on toward the drier. A secohd coating of adhesive, known as sizing coat, is usually given to the dry abrasive-coated sheet.

In Figure 5, there is shown an abrasivedisk 2|,-

of the type covered by this invention, in a typical manner of use. It is shown employed in-abrading a curved surface of work piece W, and is mounted on driven flexible pad 22 so that it can flex as it comes in contact with the work, andthus have its abrasive surface assume momentarily at such zone of contact the contour ofthe work surface. Pad 22 is partially backed by cgnventional backing plate 23,.and is driven by plate}! and front plate 21, secured to the pad and to each other by machine screws 26. Plate 24 has internally threaded hub 25- thereon, sothat it can be power driven, either mounted rigidly on a motor shaft or on a driven flexibleshaft. Abrasivedisk II is lines concentric with the axis of the disk; -(2') radial tensional and compressional forces as the disk or work is traversed to cover the work surface, and (3) torsional forces resulting from the manner of driving the disk. Unless the backing material employed in the abrasive disk can endure such forces for a reasonable length of time, it is unsuitable, both for economic reasons and for the before-noted danger which attends use of a disk having a weak or weakenedbacking material.

It is obvious that an abrasive belt is likewise subjected to severe forces of several kinds, such as rapidly repeated bending 'and tension along the length of the belt. The backing material used in the abrasive belt must likewise endure such forces for a considerable length of time in order to make its use feasible.

In Fig. 6 is shown a prior art abrasive disk D which shows signs of failure. This disk is composed of paper, cloth glued thereon, and abrasive grains glued to the cloth. In a disk having a. backing composed in a large part by a paperboard showing marked difl'erences in directional properties, as in the disk shown in Fig. 6, failure results in radial lines R and concentric lines C, said concentric lines C being roughly parallel to the direction of travel T of the paperboard through the paper making machine. This is so because more fibres line up in the paper -in the direction of its travel through the machine than transversely of such direction. Consequently, the paper is stronger in tension along line T than transverse to it, and also withstands flexure in a line across the direction T much better than it backed abrasive of the present invention employing adhesive layers between the paper laminations of the overbeaten kraft paper. The abrasive is denoted by character 30,3l denotes an adhesive modification.

- In Fig. 8 the upper layers 30-33 of the disk are the same as those in Fig. 7. Paper layer 34 is overbeaten kraft fibre paper, with or without adhesive layers between the paper'laminations. Layer 35 is the layer of adhesive applied'by the apparatus of Fig. 2 during drying of the paper,

as above described.

Fig. 9 shows in enlarged cross-section an abrasive belt ,made in'accordance with the-present invention. Overheaten kraft fibre paperboard 39,

' paper by the apparatus of Fig, 2. IA thin layer 31 with or without adhesive applied between laminations thereof, has a layer of adhesive 38 on one surface thereof, applied during drying of the of adhesive is put on the dried adhesive layer 38,

and abrasive grain 38 is put on layer 31. The

grain 38 penetrates layer 31 to some extent, and

rests on or close to layer-l8. Because the adhesive 38- is partially impregnated in the paper, it presents a rigid substantial foundation or backing for the abrasive grains. .The abrasive grains, be-

ing thus held substantially unyieldingly against the work, cut very efliciently.

The belt may be further strengthened by the addition of a further adhesive layer such as layer 3|, applied while the paper is still moist, on the tothebacking.

back of paper 39. There may be added also on such back surface a layer of cloth adheslvely held thereto.

The product of the present invention compares favorably in length of life with the more expensive backed abrasive with "vulcanized fibre" backing. present invention whether it has the backing made of overbeaten krait fibre with adhesive layers between paper laminations, whether the backing is laminated overbeaten kraft fibre without adhesive layers between laminations but coated with adhesive on one or both sides durin drying, or whether the backing has both these features. Furthermore, it has done away with the types of failure shown in the prior art as illustrated by Fig. 6 in connection with a disk and as described above in connection with a belt. The adhesive placed between laminations of the paper while they are wet penetrates the paper and thus stiffens and strengthens it when dry. In addition the adhesive produces a strong bond between paper iaminations, eliminating any tendency for the paper to separate into layers during use. The outer adhesive coating or coatings on the paper made of highly overbeaten k'raft pulp, also contribute greatly to the strength of the paper and are suiflcient, when used by themselves. on a, paperboard made from overbeaten kraft pulp to yield a product well suitedfor use in a backing for abrasive disks or belts. The outer coating layer being put on while the paper is wet, sinks into the paper to a large degree and becomes incorporated in it, thus greatly strengthening the paper. When the abrasive grain is usedbn such outer impregnating adhesive layer it cuts very efilciently, as has been noted in conneotion with an abrasive belt, because of the firm foundation for the grain which said impregnating adhesive layer aflords.

Having fully described my invention, I claim:

1. A flexible backed abrasive comprising a This is true of the abrasive of the aasasoo 6. The method of manufacturing flexible backed abrasives which comprises preparing an aqueous suspension of kraft pulp fibers highly hydrated by prolonged beating, forming the hydrated sticky pulp fibres into a thick sheet andpartially drying said sheet, attaching a layer of hardenable adhesive to one side of the sheet before it is completely dry, drying the sheet and hardening the adhesive, attaching, a layer of cloth to the side of the sheet not previously coated with adhesive, and attaching abrasive parbacking of which the main constituent is a layer of laminated paperboard formed from an aqueous suspension of wood pulp fibers highly hydrated by prolonged beating in which the laminations have added adhesive layers between them, and a layer of abrasive grains adhesively attached to the backing.

2. A flexible backed abrasive comprising a backing of which the main constituent is a layer of laminatedpaperboard formed from-an aqueous suspension of wood pulp fibers highly h drated by prolonged beating, at least one of the lamina of said paperboard having a layer ,of added adhesive on at least one side thereof, and

a layer of abrasive'grains adhesively'attached 3. A flexible backing of which the main constituent is a layer of laminated paperboard formed from an aque-. 'ous suspension of woodpulp fibers hi hly hy-v drated by prolonged beating in which the laminations have added adhesivelsyers between them,

said paperboard hayilll a layer of added adhe sive on at least one side thereof, and a layer of abrasive .grains adhesively attachedto the 4. A flexible backed abrasive comprising a layer of laminated p perboard formed from an backed abrasive comprising .a

aqueous suspension of kraft pulp fibers highlyhydrated by prolonged a layer'ofcloth attached to one face of the paperboard. a we:

ofaddedadhcsivoontbesidoofthopaperboard 15 ticles to said cloth layer.

'l. The method of manufacture of flexible backed abrasives which comprises highly hydrating kraft pulp fibers by a prolonged beating until the fibres are adhesive, forming the coatedfibres into a thick sheet and partially drying said sheet, applying a layer of hardenable adhesive to one side of the sheet before it is completely dry. drying the sheet and hardening the adhesive,

and adhesively attaching abrasive grains to thesaid sheet.

8. The method of manufacture of flexible backed abrasives which comprises highly hydrating kraft pulp fibers by subjecting them to a prolonged beating until the'fibres are adhesive,

forming the fibres into a thick sheet by alternately depositing successive thin layers of said fibres and glue, partially drying said sheet, attaching a layer of glue to at least one side of the sheet before.it is completely dry, further drying said sheet, contacting the sheet with a tanning solution suitable for at least some of the glue layers employed, attaching abrasive par- I ticlestothe said sheet.

9. The method of manufacturing flexible backed abrasives which comprises subjecting kraft pulp fibers to a prolonged beating until the fibers become highly hydrated and adhesive,

depositingalternate layers of the said fibers. and an adhesive to build up a relatively thick sheet,

drying said sheet, attaching 'a layer of cloth to one side of the sheet by means of an adhesive. any: attaching abrasive particles to the said cloth 1'.

1c. The method of manufacturing fiexible 'back'edj-abrasives which comprises subjecting kraft pulp fibers to a prolonged bea until the fibers become highly hydrated and esive, depgitlnl" alternate layers of said fibers and an adhesive to build up a relatively thick sheet, drying said sheet, and attaching abrasive particles to the sheet.

11..The method of. manufacturing flexible backed abrasives which comprises subjecting kraft pulp'fibers'to a prol nged beating until they becomrhighly hydrated and'adhesive, depositing'alternatc layersofithe said fibers and an, adhesive. to build up a relatively thick sheet,

treating the adhesivelayers to make them waterrasistant, and attaching s cc Y mm c. mm.

abrasive particles to the 

